1. Field of the Invention
The present invention relates to a node device having interface for virtual connection-oriented network, and a scheme for sharing a common virtual connection identifier between end-nodes in forms of such node devices.
2. Description of the Background Art
Currently, a CSR (Cell Switch Router) has been proposed as a high speed router for connecting ATM (Asynchronous Transfer Mode) networks. This CSR has a built-in ATM switch for realizing a function of transfer in cell units in addition to a usual function of transfer in IP (Internet Protocol) packet units.
By utilizing this cell transfer function, it is possible to realize high throughput and low delay communications by taking full advantages of ATM according to the need, even in a case of passing through a router at an IP subnet boundary. Namely, in the ATM Internet formed by using CSRs, a packet assembling and a hop by hop IP transfer processing based on destination IP address are carried out similarly as in a conventional case for some communication at each CSR to be passed through, while a cell based transfer processing by only referring to VPI/VCI of a received cell is carried out for some other communication at each CSR to be passed through so as to omit IP transfer processing for each packet as much as possible. In the following, a VC (Virtual Connection) for realizing a hop by hop packet transfer will be referred to as a default VC, and a VC for realizing a cell based transfer will be referred to as a dedicated VC.
In the cell based transfer, it is not allowed to refer to a content of a packet so that a packet transfer without referring to a content of a packet is realized by using different dedicated VCs for different packet flows.
Also, in the cell based transfer, it is not allowed to refer to a content of a packet so that there is a need to exchange a message indicating that a packet with which destination is to be transferred through which dedicated VC, between neighboring nodes in advance. An identifier for identifying each dedicated VC which is necessary in this message will be referred to as VCID. Note that it is necessary for VCID to be a common identifier for both end-nodes of the dedicated VC.
In general, in ATM, a virtual connection identifier value (VPI/VCI) described in a cell header is different at both ends of the virtual connection. For this reason, it is necessary to provide a new identifier called VCID which is different from VPI/VCI and a scheme for establishing correspondence between the virtual connection identifier and the common identifier.
As a scheme for sharing an identical identifier at both ends, there is a scheme for notifying an identical identifier by using an ATM signaling message. For example, by using BLLI (Broadband Low Layer Information) as a common identifier (VCID), it is possible to establish correspondence between the virtual connection identifier and the common identifier.
However, this scheme is associated with a problem that a region available for the common identifier becomes small when a region available in the ATM signaling is small (BLLI field only has a 7 bit region that can be used by a user, for example), so that a number of dedicated VCs that can be used simultaneously will be limited.
On the other hand, there is also a scheme for establishing correspondence between the virtual connection identifier and the common identifier by sending a message containing the common identifier (VCID) through a dedicated VC (in-bound), as disclosed in xe2x80x9cFlow Attribute Notification Protocol (FANP) Specificationxe2x80x9d, draft-rfced-info-nagami-00.txt, IETF Internet Draft (February 1997).
However, this scheme is associated with a problem that it is difficult for a node that carries out the cell based transfer such as CSR to transmit a message packet with respect to a VC which is already carrying out the cell based transfer. This is because of the following.
First, in a case of transmitting a packet to an ATM network, there is a need to disassemble a packet into ATM cells (48 bytes). There are several methods for disassembling a packet into ATM cells, but a method called AAL5 is customarily used in general. This method divides a packet into segments in ATM cell (48 bytes) sizes, and attaches an xe2x80x9cend of packetxe2x80x9d marking only to the last ATM cell of this message. When ATM cells obtained by this method are received consecutively, a receiving node can recognize the last ATM cell of the packet and assemble the packet from received ATM cells. However, when another ATM cell unrelated to the disassembled packet gets mixed in a middle, it is impossible to assemble the packet from ATM cells.
Now, inserting a packet in order to attach a VCID to a VC that is carrying out the cell based transfer at CSR is equivalent to mixing ATM cells of a packet for VCID exchange in a middle of ATM cells belonging to packets transferred by the cell based transfer. Consequently, simply sending a message packet into a VC that is carrying out the cell based transfer causes cell mixing and thereby makes it impossible to assemble packets at a receiving node.
A need for sending a VCID exchange packet into a VC that is already carrying out the cell based transfer also arises at a time of set up of a virtual connection for multicast, for example. Namely, while the cell based transfer is carried out for participants of multicast by using an already set up virtual connection for multicast, if a new leaf for a new participant (node) is to be added to this virtual connection, a message packet to this new node would have to be sent through that VC which is already carrying out the cell based transfer according to the conventional scheme for sending a message in-bound.
It is therefore an object of the present invention to provide a node device and a scheme for sharing a common virtual connection identifier between end-nodes, which enable sharing of a common identifier at both end-nodes of a virtual connection for which a common identifier is required, without sending a message in-bound through that virtual connection, while attaching a sufficiently large common identifier to that virtual connection.
According to one aspect of the present invention there is provided a node device, comprising: an interface for a virtual connection-oriented network; a first message exchange unit for exchanging a first message which contains a first identifier for provisionally identifying a virtual connection commonly between said node device and a neighboring node device, at a time of setting up the virtual connection through the interface; a management unit for managing a correspondence between the first identifier and a second identifier having a larger information size than the first identifier for formally identifying the virtual connection commonly between said node device and the neighboring node device; and a second message exchange unit for transmitting or receiving a second message which contains the second identifier in a form that enables establishing of a correspondence between the first identifier and the second identifier, through another virtual connection different from the virtual connection to be set up.
According to another aspect of the present invention there is provided a method for sharing a common virtual connection identifier between neighboring nodes, comprising the steps of: exchanging a first message between the neighboring nodes, the first message containing a first identifier for provisionally identifying a virtual connection commonly between the neighboring nodes, at a time of setting up the virtual connection; exchanging a second message between the neighboring nodes, the second message containing a second identifier having a larger information size than the first identifier for formally identifying the virtual connection commonly between the neighboring nodes, in a form that enables establishing of a correspondence between the first identifier and the second identifier, through another virtual connection different from the virtual connection to be set up; and managing a correspondence between the first identifier and the second identifier at each of the neighboring nodes according to the first message and the second message so as to share the second identifier between the neighboring nodes.
According to another aspect of the present invention there is provided an article of manufacture, comprising: a computer usable medium having computer readable program code means embodied therein for causing a computer at a node device to function as a system that enable sharing of a common virtual connection identifier between neighboring nodes, the computer readable program code means includes: first computer readable program code means for causing said computer to exchange a first message which contains a first identifier for provisionally identifying a virtual connection commonly between said node device and a neighboring node device, at a time of setting up the virtual connection; second computer readable program code means for causing said computer to manage a correspondence between the first identifier and a second identifier having a larger information size than the first identifier for formally identifying the virtual connection commonly between said node device and the neighboring node device; and third computer readable program code means for causing said computer to transmit or receive a second message which contains the second identifier in a form that enables establishing of a correspondence between the first identifier and the second identifier, through another virtual connection different from the virtual connection to be set up.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.